Multi-rotor UAV flight control method and system

ABSTRACT

Disclosed herein is a method and system for flying rotary wing drone. An add-on flight camera that is free to rotate around the vehicle&#39;s yaw axis is attached to the drone. The flight camera is automatically looking in the direction of its flight. The video from the flight camera is streamed to the operator&#39;s display. Thus the rotary wing drone can fly in any direction with respect to its structure, giving the operator a first person view along the flight path, thus keeping high level of situational awareness to the operator. The information required for controlling the camera orientation is derived from sensors, such as GPS, magnetometers, gyros and accelerometer. As a backup mode the information can be derived from propeller commands or tilt sensors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit ofco-pending U.S. patent application Ser. No. 15/873,115 filed Jan. 17,2018 which claims the benefit of PCT/IL2016/050814 filed Jul. 25, 2016which claims the benefit of U.S. Provisional Patent Application62/197,569 filed on Jul. 28, 2015, all of which are incorporated hereinby reference.

TECHNICAL FIELD

The present invention generally relates to the field of remotelycontrolling Unmanned Aerial Vehicle (UAV), and more particularly,controlling remotely the flight of multi-rotor UAV or ducted-fan UAV.

BACKGROUND ART

Multi-rotor UAV (and multirotor copiers general) configurations havebecome popular in UAV (Unmanned Aerial Vehicle) as payload carryingplatforms. They are known for their simplicity and for their highmaneuverability. They are used for military as well as for civilianpurposes. Such multi-rotor UAVs are sometimes also referred to astri-copter, quadcopter, hexa-copter and octocopter, quads and drones.From now on we refer to these UAV's as Rotary Wing Drones.

The most difficult part of flying rotary wing drones is controlling themremotely. This difficulty arises from decrease of the situationalawareness of the operator, which in turn, significantly decreasesworking efficiency and at the same time increases risks. Low workingefficiency results in high operating costs, and risks present evenhigher costs associated with collision inflicted hardware damages andhuman injuries.

The situational awareness of the operator is dependent on two mainfactors: the quality of input from his senses and hisattention/concentration levels. Decreasing any of the two dramaticallyreduces the situational awareness of the operator and hence his abilityto control the rotary wing drone and to accomplish the mission'spurpose.

Remote controlled rotary wing drones are mainly used to photograph anddocument various subjects in civilian and in military applications, suchas reconnaissance missions, social events, sport events, scenery, moviescenes, maintenance of buildings, bridges, and pipelines, and alsoaccidents, fires and home security scenes. These missions are performedby an operator/pilot which has to fly and control the rotary wing droneremotely by looking up to the sky to watch it and at the same time keepthe documenting camera pointed and focused on the documented subject bywatching its output on a small screen to which the film is transmitted.Attempting to simultaneously perform those two distinct operations,which are taking place in different reference systems with differentrate of change, severely harm the operator's attention/concentrationlevels.

Moreover, remotely flying a rotary wing drone, where the operator is notonboard, intrinsically deprives the operator of sensations of speed,acceleration, noise, distance, three-dimensional image of space,directions (right/left), direction of propagation (forward/backward,to/from) and inclination (pitch/roll). Additionally, the distancebetween the operator and the rotary wing drone, optically converge allobjects in the distance such that the operator can't distinguish therotary wing drone from objects surrounding it. All these dramaticallydegrade the situational awareness of the operator and thus his abilityto perform the mission efficiently and safely.

In fixed wing UAVs there is an intrinsic continuous flight path due tothe aeronautical characteristics of the fixed wing UAV. This helps theoperator create and maintain a better idea of the direction of movementof the UAV based on this path that is registered in his mind and thusallows him to predict the location and direction of movement to come. Incontrary, because rotary wing drone can change the direction of itsflight and its speed abruptly, the ability to predict the location anddirection of propagation of the rotary wing drone is severely tampered,and hence also the operator's situational awareness.

Hence a solution to the problem of the degradation of situationalawareness of operators of rotary wing drones is needed.

SUMMARY OF INVENTION Technical Problem

Rotary wing drones are frequently used for documenting objects. Usually,the documenting camera is attached to the rotary wing drone pointing inthe direction the its front (its roll axis). The camera is usuallygimballed on the pitch and roll, and sometimes it can be rotated by theoperator in the yaw axis. The main task of the ground operator is topilot the vehicle to obtain the required documentation information.Often, the operator needs to fly the rotating wing drone in a directionwhich is not aligned with its roll axis. As an example the operator isasked to film a line of olive trees in an orchard in order to evaluatethe amount of fruit. In order to achieve it the operator needs to flythe rotary wing drone along the lines of the trees, where its front withthe documenting camera points to the trees while it flies to its side.Thus, simultaneously the operator has to look up to the sky to watch therotary wing drone and to keep the documenting camera pointed and focusedon the documented subject by watching its output on a small screen towhich the film is transmitted. Thus the situational awareness of theoperator is dramatically decreased, which leads to increased risk, andperformance degradation.

Solution to Problem

The solution to the problem is to add a video camera, called FlightCamera, that is free to rotate around the rotary wing drone's yaw axis,and to automatically continuously point its field of view in thedirection of propagation of the rotary wing drone. The video from theflight camera is streamed to the operator's display.

Advantageous Effects of Invention

The disclosed invention dramatically improves the efficiency and safetyof flying rotary wing drones. It does so by returning a high level ofsituational awareness to the operator. As a result it increases flightsafety and reduces the operational costs.

The objective of the disclosed invention is to add the ability to flyrotary wing drone from a First Person View (FPS) perspective (flyingfrom the cockpit) regardless of the direction of the vehicle's body.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a top view of a typical rotary wing drone.

FIG. 2 shows a top view of rotary wing drone with the added nightcamera.

FIG. 3 shows a block diagram of one embodiment of the flight camera.

FIG. 4 shows a block diagram of one embodiment of the flight cameraalignment.

FIG. 5 presents another implementation of the disclosed invention.

DETAILED DESCRIPTION

The invention will be described more fully hereinafter, with referenceto the accompanying drawings, in which certain possible embodiments ofthe invention are shown. The invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather these embodiments are provided sothat the disclosure will be thorough and complete, and will fully conveythe scope of the invention to those skilled in the art.

The description that follows refers to a multi-rotor UAV as an example,albeit, the same solution is applicable to multirotor UAVs, unmannedhelicopters and to ducted-fan air vehicles. All these UAV types arereferred to as Rotary Wing Drone.

Throughout the rest of the specifications and the claims we shall usethe following terms as they are defined hereunder.

Natural plane is a plane that passes through the drone's center ofgravity and is perpendicular to the yaw axis of the rotary wing drone.

Local coordinates are Cartesian coordinates fixed relative to thestructure of the rotary wing drone. Usually they are aligned withdirection of the inertial measurement unit's sensors.

The direction of the drone's flight is the direction of its propagation.

Geographic coordinates are the coordinate system in which the GPSprovides information on the flight direction of the rotating wing drone.

We further define first-person-view, also known as remote-person-view,or simply video piloting, as the method used to control a remotecontrolled vehicle from the driver's or pilot's view point as if theywere sitting on board the vehicle.

FIG. 1 presents a top schematic view of a typical rotary wing drone 100having four rotors. It is comprised of a body 102, to which four motorarms 104 a, 104 b 104 c and 104 d are symmetrically attached. At the endof each motor arm 104 a, 104 b, 104 c, 104 d, a propeller 106 a, 106 b,106 c, 106 d is mounted. The rotors are driven by respective motors 108a, 108 b, 108 c and 108 d. The propeller can be either with fixed pitchor variable pitch. The propellers of each diagonal rotate in the samedirection i.e. rotors 106 a and 106 c rotate in one direction and rotors106 b and 106 d rotate in opposite direction. The motion of the rotarywing drone is controlled by adjusting the spin speeds and optionally thepitch of its propellers. All the required electronic units are attachedto the body of the rotary wing drone 102. As a minimum it contains apower unit, a motor control and drive unit and ground communicationunit.

A top view of a rotary wing drone with the added flight camera unit,according to the invention is shown in FIG. 2. A video camera unit 210is mounted on the body is comprised of a video camera 220 attached to agimbal that is free to rotate around the yaw axis of the rotary wingdrone. The yaw axis in the figure is perpendicular to the plane of thepaper. The plane of the paper also represents the natural plane. Thecamera is controlled to look in the direction of the projection of theflight direction on the natural plane V—230. The camera unit containsthe required electronics that supports its operation. Note, that duringcalibration, the representation of the yaw axis in the local coordinatesystem has to be determined, as well as the zero reference direction ofthe video camera.

A detailed block diagram of the flight camera unit 350 is presented inFIG. 3. The flight-camera-unit 350 is composed of a flight camera 320firmly attached to 360° CW/CCW rotating camera pedestal 310. The camerapedestal is driven by a pedestal motor 354 which is controlled bypedestal servo controller 352. The pedestal servo controller accepts asa command the angle Ψ of the required center of the field of view of thecamera. The flight camera unit includes a video transmitter 360, thattransmits the video to a ground receiver and monitor 390. The signals toand from the camera are channeled via slip rings 356 and 358, one forthe video signal and one for the power. All components get the energyfrom a power unit 362.

Block diagram of one embodiment of the invention is presented in FIG. 4.The flight-camera-system is comprised of a sensors unit 410, processingunit 420 and the flight camera unit 350. The sensors unit provides itsdata to a processing unit 420. The processor unit 420 computes the angleΨ to which the flight camera has to be rotated in order to point in thedirection of vehicle's direction of flight in the natural plane, and itprovides driving signals to the flight camera unit 350 which rotates thecamera to the dashed direction. All components get their power from apower unit 450. The power unit can be independent or it can get itsenergy from the power source of the vehicle. Note that the sensors usedby the system can be either add on sensors, or the rotary wing dronebuilt in sensors.

The sensors unit 410 is comprised, as a minimum, of a GPS andmagnetometers, and can include additional sensors such as accelerometersand gyros. The sensors provide the data required for the computation ofthe direction of the flight in local coordinates. The use of theadditional sensors, results in improved accuracy in the positioning ofthe flight camera. It is important to note that the field of view of theflight camera is much wider than the magnetic deviation, so the errorinduced by the use of magnetometers and not the geographical north ismeaningless. If accurate INS system is used, there is no need for themagnetometers.

FIG. 5 presents another implementation of the disclosed invention. Thisimplementation can be used as a backup mode when GPS signals areblocked, such as in a building, or when the drone's flight is notaffected by winds. In this implementation the direction of flight of therotary wing drone is computed by the processor from the commands 522sent to the propellers 510 by the flight controller 520

In a similar way, the flight direction of the rotary wing drone, can beevaluated by tilt sensors attached to it. This method is also used asbackup mode or when GPS signal is unavailable.

What has been described above are just a few possible embodiments of thedisclosed invention. It is of course, not possible to describe everyconceivable combination of components and/or methodologies, but one ofordinary skill in the art may recognize that many further combinationsand permutations are possible. Accordingly, the invention is intended toembrace all such alterations, modifications, and variations that fallwithin the spirit and scope of the invention.

The invention claimed is:
 1. A flight camera comprising: a. asingle-elevation camera pedestal attachable without a mast to a drone,wherein the pedestal can rotate in a clockwise or counterclockwisedirection; b. a video camera attached to the camera pedestal, whereinthe video camera streams to the drone's operator a first-person-viewvideo in the direction of the drone's flight, regardless of the drone'syaw; c. a processing unit that computes an angle Ψ, wherein angle Ψ isthe angle to which the video camera has to be rotated in order to pointin the direction of the drone's direction of flight; d. a pedestal servocontroller for receiving the angle Ψ from the processing unit; e. apedestal motor in communication with the pedestal servo controller,wherein the pedestal motor turns the camera pedestal to the angle Ψ; andf. a video transmitter that transmits the video to a receiver fordisplay on a drone operator's monitor.
 2. The flight camera of claim 1wherein the video camera's field of view is aligned with the projectionof the drone's flight direction on the natural plane.
 3. The flightcamera of claim 1 wherein the pedestal can rotate up to 360 degrees in aclockwise or counterclockwise direction.
 4. A rotary wing dronecomprising: a. a first and second single-elevation camera pedestals,each attached without a mast to the drone, wherein the first pedestalcan rotate in a clockwise or counterclockwise direction; b. a firstcamera attached to the first camera pedestal, wherein the first camerastreams to the drone's operator a first-person-view video in thedirection of the drone's flight, regardless of the drone's yaw; c. asecond camera attached to the second camera pedestal; d. a processingunit that computes an angle of rotation for each pedestal, wherein angleΨ is the in the direction of the drone's flight regardless of thedrone's yaw; e. a pedestal servo controller for controlling each angleof rotation, wherein while the first video camera is pointed at angle Ψ,the second video camera is simultaneously: i. pointed at a fixed anglerelative to the drone; or ii. tracks a specific location; f. a firstpedestal motor in communication with the pedestal servo controller forrotating the first camera and a second pedestal motor in communicationwith the pedestal servo controller for rotating the second camera,wherein the first pedestal motor turns the camera pedestal to angle Ψand the second pedestal motor turns the camera pedestal to either thefixed angle relative to the drone or a specific location; and g. a videotransmitter that transmits the video to a receiver for display on adrone operator's monitor.
 5. The rotary wing drone of claim 4 whereinthe second pedestal cannot rotate 360 degrees in a clockwise orcounterclockwise direction.
 6. The rotary wing drone of claim 4 whereinthe first video camera's field of view is aligned with the projection ofthe drone's flight direction on the natural plane.
 7. The rotary wingdrone of claim 4 wherein the first video camera is pointed automaticallyand continuously at angle Ψ.
 8. The rotary wing drone of claim 4 whereinthe first pedestal can rotate up to 360 degrees in a clockwise orcounterclockwise direction.
 9. A method for remotely piloting a rotarywing drone flying in any direction, by streaming to the drone's operatora first-person-view video in the direction of the drone's flight,regardless of drone's yaw, the method comprising: a. fitting the dronewith a flight video camera capable of rotating around drone's yaw axis;b. acquiring the projection of drone's flight direction on the naturalplane in local coordinates; c. automatically and continuously turningthe flight video camera so that the center of its field of view isaligned with the projection of the drone's flight direction on thenatural plane; and d. streaming the video from the flight video camerato an operator's client.
 10. The method of claim 9 wherein the flightcamera cannot remain at a fixed angle with respect to the helicopter.11. The method of claim 9 wherein the flight camera cannot continuouslytrack a single location.